Astronomers have found the remains of a once-massive star, now transformed into a solid diamond five times bigger than Earth.
The object circles a pulsing companion star about 4,000 light years from Earth in the constellation Serpens (The Snake), which lies about one-eighth of the way toward the center of the Milky Way galaxy.
Astronomers noticed that the steady pulses of energy coming from the star, known as J1719-1438, were regularly and minutely disturbed, a phenomenon caused by the gravitational tug of another, smaller circling object.
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By measuring the pattern, scientists were able to figure out how far away the second object circles and its mass, leading to the realization that they had found a bizarre binary system, with one partner reduced to a diamond core.
"In this case, something with the mass of our sun has evolved to be something the mass of a planet -- quite extraordinary," astronomer Michael Keith, with the Australia Telescope National Facility, wrote in an email to Discovery News.
The companion to J1719-1438 never got big enough to produce elements much heavier than carbon, so after its lighter-weight hydrogen and helium were stripped away that would leave a solid core of carbon -- diamond.
"Due to the immense pressure, the carbon will be in a dense crystal-like structure, although much more closely packed than in a diamond on Earth," Keith said.
The system is now stable, with no evidence that it will change for billions of years.
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"Of course, this also means that it could well have been around for a long time, just waiting for us to find it. Since it's likely to last for longer than the Earth or the sun, I would say that in this case, a diamond really is forever," Keith said.
The diamond planet was found as part of an ongoing search for pulsating stars, known as pulsars, which scientists like to use as probes.
"We'd like to find a pulsar with a black hole companion," Michael Kramer, director of the Max Planck Institute for Radio Astronomy in Bonn, Germany, told Discovery News. "It's the exotic case that tell us most about the laws of physics and what's going on in the universe."
The research is published in this week's Science.